The invention relates to an optoelectronic inclination sensor for determining the inclination of a reference plane relative to the horizontal, particularly for the simultaneous acquisition of inclinations about two axes according to the preamble of claim 1.
An optical inclination sensor according to the preamble comprises a sensor body which is partially filled with a liquid, wherein the liquid layer provides an optical boundary (for example, liquid/air), which forms a horizon. The reference plane whose inclination is to be determined is formed on the sensor body, for example, as bottom surface. Moreover, a light source for the emission of a light beam which passes through the liquid and is directed onto the boundary is provided. An optical sensor surface, which is used for detecting the light beam reflected by the boundary, is arranged inside or outside of the sensor body. Finally, a processing unit for determining the inclination of the plane as a function of the light quantity received by the optical sensor surface is provided.
DE 198 19 610 C1 describes an optical inclination measuring device, wherein a housing is filled with a transparent liquid which changes the direction of an optical ray beam depending on the inclination. A light source for illuminating a structure or for generating a light point is provided, which directs light beam onto the liquid/air boundary in such a manner that its reflection is incident on a sensor surface and detected there. The optical means for representing the structure or the light point or light spot are arranged on the bottom side of the bottom of the housing or they are a component of said bottom. Moreover, said optical means are formed by a single element which couples light in or out and reproduces the structure or the light point.
From DE 20 2004 010 922 U1, an inclination sensor according to the preamble with a combined glass-liquid prism is known, wherein the light beam undergoes total reflection at the liquid horizon, so that the deflection angle is twice as large as the angle of incidence.
DE 20 2007 002 771 U1 describes a two-axis optical inclination measuring device having an LED as radiation source, a housing with a liquid forming a horizon, a sensor for receiving the radiation as well as optical means with a beam path for representing the radiation on the sensor. The device comprises, moreover, a processing unit for determining the inclination from the signals emitted by the sensor. The optical means form a mark on the sensor, in such a manner that the inclination can be determined in two orthogonal axes from the position of the marks on the sensor. In the case of reflection at the liquid horizon, the radiation should be reflected substantially perpendicularly. In the case of perpendicular impingement of the light beam on the boundary at the liquid horizon, the light is in large part expected not to be reflected, and exits instead at the boundary with varying degrees of refraction.
FR 2 868 834 B1 describes a two-axis inclination sensor, which comprises a sensor body having in sections a spherical shape, in which a liquid forming a horizon is arranged. The sensor body has a light beam source on its rotation axis, which directs a ring light beam onto the liquid surface. Said ring light beam is reflected at the surface and detected by means of sensors. The sensors are arranged outside of the sensor body. The sensor body comprises four windows through which the reflected light beams can impinge on the sensors. The windows are provided either on the bottom side of the sensor body or on the spherical lateral surface. The sensors here embody north-south or east-west axes.
Inclination measuring devices with bubble levels are also known. For a two-dimensional measurement, circular bubble levels are used. An inclination sensor having such a circular bubble level is described, for example, in DE 10 2005 056 736 B4. In the case of a circular bubble level, for the electronic determination of the inclination, an emitter-receiver component assembly is arranged above the glass cover, wherein the light emitted by the emitter is at least partially totally reflected at the glass cover/air bubble boundary when the air bubble is centered. The disadvantage of the bubble level sensors results particularly from the fact that the surface against which the bubble level is applied presents a curvature with a certain radius. The curvature is here adapted to the sensitivity requirements of the bubble level, and it is produced by means of loops, which roughens the surface to a certain extent, as a result of which the gas bubble may tend to bounce, and the accuracy of the sensor is affected. Due to the shape of the gas bubble and the curvature of the glass cover, a nonlinear characteristic line of the sensor is obtained. In addition, the size of the gas bubble is dependent on the temperature of the sensor, which has a disadvantageous effect on the range of application of such sensors.
From the journal “Technisches Messen,” Edition 75, 2008, a laser-based emitter-receiver component assembly with integrated micro-optics for measuring scattered light is known. The emitter-receiver component assembly is implemented in a square silicon substrate, in which rotation symmetric photodiode segments have been introduced. The latter surround a central deep etching in which a laser is located. On the silicon substrate, a spacer medium is applied, which consists of a glass that is not permeable for the wavelength of the laser. Above the laser and above the photodiodes, the spacer part is provided with perforations. In this manner, the source and the receiver are optically isolated from each other. The micro-optical system is accommodated in the central area of the perforation. The sensor is completed by an optics carrier. The latter consists, on the one hand, of a carrier made of a chemically resistant material. On the other hand, light impermeable and structurable diaphragms are arranged on the bottom side of this carrier. The micro-optical system is located on this diaphragm structure. It is in the shape of a ring with radially symmetrical aspherical cross section (ring lens).